Here is the DIY to utilize BMW provided OEM Sharkfin GPS Antenna for your aftermarket Headunit. (ex. Dyanavin)
Contrary to popular belief, most vehicles that did not come with I-Drive does indeed have a GPS receiver in the Sharkfin antenna in conjunction with other receivers such as radio, cell, etc etc...
These connectors are all located in the trunk compartment
(Pull the trunk "secret compartment" lid outward and you will see this
1) Items you need to purchase:
1. SMA Straight Male Crimp for RG-174 Cable
2. Fakra Plug Crimp Connector
3. RG-174 Coaxial Cable
*Note* Remember to purchase enough length of the coaxial cable to reach from the dash to the trunk about 5 meters (16 feet)
2) Connect the SMA Male Crimp and Fakra Plug to each end of the coaxial cable
3) Wire the cable from your Dynavin unit to the trunk through the center console:
Run the cable from the CCC, along the passenger side of the center console wiring, and underneath the back driveshaft tunnel. The carpet is extremely tight here, so use a couple of large screwdrivers to make a path for the coaxial cable to pass through.
4) The blue connector is originally connected to the box shown in the picture.
Pull that plug out and connect your fakra plug.
5) Test to see if the GPS signal works